1. Field
The embodiments discussed herein are directed to a demodulator.
2. Description of the Related Art
In an optical fiber communication adopting a wavelength division multiplex (WDM) system, an optical signal modulated by a differential phase shift keying (DPSK) system or the like is demodulated by a demodulator that has a delay interferometer. For example, in a delay interferometer using the DPSK system, optical paths separated by splitting are made different in geometrical length, thereby providing a delay.
In the delay interferometer, when the ambient temperature changes, optical components, etc. expand or contract, changing the optical phase of an optical signal. Accordingly, the optical phase has to be adjusted. Conventionally, a simultaneously monitoring of the electric current in a light receiving element and feed-back-controlling a phase is disclosed. Additionally, conventionally a demodulation technology using a delay interferometer is disclosed.